Control system for reducing nitrous oxide (“N2O”) after selective catalytic reduction (“SCR”) device light-off

Abstract

An exhaust gas treatment system for an internal combustion engine is provided having an exhaust gas conduit, an oxidation catalyst (“OC”) device, a selective catalytic reduction (“SCR”) device, and a control module. The internal combustion engine has at least one operating parameter. The exhaust gas conduit is in fluid communication with, and is configured to receive an exhaust gas from the internal combustion engine. The exhaust gas contains oxides of nitrogen (“NO x ”) and hydrocarbons. The exhaust gas has an exhaust gas temperature. The OC device is in fluid communication with the exhaust gas conduit, and is activated to induce oxidation of the hydrocarbons in the exhaust gas. The OC device has an oxidation catalyst compound disposed thereon that is selectively activated at a specified temperature range for converting nitrogen oxide (“NO”) to nitrogen dioxide (“NO 2 ”) at a specified percentage.

What is claimed is: 
     
       1. An exhaust gas treatment system for an internal combustion engine, the internal combustion engine having at least one operating parameter, comprising:
 an exhaust gas conduit in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine, the exhaust gas containing oxides of nitrogen (“NO x ”) and hydrocarbons, the exhaust gas having an exhaust gas temperature; 
 an oxidation catalyst (“OC”) device in fluid communication with the exhaust gas conduit, the OC device activated to induce oxidation of hydrocarbons in the exhaust gas, the OC device having an oxidation catalyst compound disposed thereon that is selectively activated at a specified temperature range for converting nitrogen oxide (“NO”) to nitrogen dioxide (“NO 2 ”) at a specified percentage; 
 a selective catalytic reduction (“SCR”) device in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas, the SCR device located downstream of the OC device, wherein the SCR device is selectively heated to a SCR light-off temperature, and wherein the overall temperature of the SCR device is represented by a SCR temperature profile; and 
 a control module in communication with the internal combustion engine and the exhaust gas treatment system, comprising:
 a control logic for monitoring the SCR temperature profile; 
 a control logic for determining if the SCR device is above the SCR light-off temperature based on the SCR temperature profile; 
 a control logic for monitoring an OC device temperature of the OC device; 
 a control logic for determining if the OC device is operating at the specified temperature range based on the OC device temperature; and 
 a control logic for adjusting at least one operating parameter of the internal combustion engine for controlling the exhaust gas temperature such that the OC device is not operating within the specified temperature range, wherein the at least one parameter of the internal combustion engine is adjusted if the SCR device is above the light-off temperature and if the OC device is operating at the specified temperature range. 
 
 
     
     
       2. The exhaust gas treatment system as recited in  claim 1 , wherein the specified percentage for converting nitrogen oxide to nitrogen dioxide is at least about fifty percent. 
     
     
       3. The exhaust gas treatment system as recited in  claim 1 , wherein the control module includes control logic for increasing the exhaust gas temperature above the specified temperature range if the SCR device is above the light-off temperature. 
     
     
       4. The exhaust gas treatment system as recited in  claim 1 , wherein the control module includes control logic for decreasing the exhaust gas temperature below the specified temperature range if the SCR device is above the light-off temperature. 
     
     
       5. The exhaust gas treatment system as recited in  claim 1 , further comprising an electrically heated catalyst (“EHC”) device in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas, wherein the EHC device is located within the OC device and is selectively activated to produce heat and induce further oxidation of the exhaust gas. 
     
     
       6. The exhaust gas treatment system as recited in  claim 5 , wherein the EHC device has an EHC oxidation catalyst compound disposed thereon for converting nitrogen oxide to nitrogen dioxide at the specified percentage at the specified temperature range, wherein the EHC device is positioned downstream of the front face of the OC device such that hydrocarbons in the exhaust gas do not substantially interfere with the generation of nitrogen dioxide by the EHC device. 
     
     
       7. The exhaust gas treatment system as recited in  claim 5 , wherein the control module is in communication with the EHC device, and wherein the control module includes control logic for deactivating the EHC device if the SCR device is above the light-off temperature. 
     
     
       8. The exhaust gas treatment system as recited in  claim 5 , wherein at least one of the oxidation catalyst compound of the OC device and the EHC oxidation catalyst compound of the EHC device is one of palladium, platinum, and perovskite. 
     
     
       9. The exhaust gas treatment system as recited in  claim 1 , wherein the SCR device is in communication with and receives and stores reductant from a reductant source. 
     
     
       10. The exhaust gas treatment system as recited in  claim 9 , further comprising NO x  sensor that is in fluid communication with the exhaust gas conduit, the NO x  sensor located downstream of the internal combustion engine to detect a NO x  concentration level at an exit of the engine. 
     
     
       11. The exhaust gas treatment system as recited in  claim 10 , wherein the control module includes control logic for determining a presence of an intermediate on the SCR device, wherein the presence of the intermediate on the SCR device is based on the NO x  concentration level at the exit of the engine and an amount of reductant that has been released by the reductant source into the exhaust gas. 
     
     
       12. The exhaust gas treatment system as recited in  claim 11 , wherein the control module includes control logic for adjusting the operating parameters of the internal combustion engine for controlling the exhaust gas temperature such that the OC device is not operating at the specified temperature range if the SCR device includes the presence of the intermediate, if the SCR device is above the light-off temperature, and if the OC device is operating at the specified temperature range. 
     
     
       13. The exhaust gas treatment system as recited in  claim 1 , comprising a hydrocarbon injector connected to and in fluid communication with the exhaust gas conduit, wherein the hydrocarbon injector is selectively activated for delivery of a hydrocarbon and formation of an exhaust gas and hydrocarbon mixture therein. 
     
     
       14. The exhaust gas treatment system as recited in  claim 13 , wherein the control module is in communication with the hydrocarbon injector, and wherein the control module includes control logic for deactivating the hydrocarbon injector if the SCR device is above the light-off temperature and if the OC device is operating at the specified temperature range. 
     
     
       15. The exhaust gas treatment system of  claim 1 , further comprising a first temperature sensor and a second temperature sensor in fluid communication with the exhaust gas conduit, the first temperature sensor situated upstream of the SCR device and the second temperature sensor situated downstream of the SCR device, wherein the control module includes control logic for monitoring the first temperature sensor and the second temperature sensor, and a control logic for calculating an SCR temperature profile based on signals from the first temperature sensor and the second temperature sensor. 
     
     
       16. An exhaust gas treatment system for an internal combustion engine, the internal combustion engine having at least one operating parameter, comprising:
 an exhaust gas conduit in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine, the exhaust gas containing oxides of nitrogen (“NO x ”) and hydrocarbons, the exhaust gas having an exhaust gas temperature; 
 an oxidation catalyst (“OC”) device in fluid communication with the exhaust gas conduit, the OC device activated to induce oxidation of the hydrocarbons in the exhaust gas, the OC device having an oxidation catalyst compound disposed thereon that is selectively activated at a specified temperature range for converting nitrogen oxide (“NO”) to nitrogen dioxide (“NO 2 ”) at a specified percentage that is at least about fifty percent; 
 a selective catalytic reduction (“SCR”) device in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas, the SCR device located downstream of the OC device, wherein the SCR device is selectively heated to a SCR light-off temperature, and wherein the overall temperature of the SCR device is represented by a SCR temperature profile; and 
 a control module in communication with the internal combustion engine and the exhaust gas treatment system, comprising:
 a control logic for monitoring the SCR temperature profile; 
 a control logic for determining if the SCR device is above the SCR light-off temperature based on the SCR temperature profile; 
 a control logic for monitoring an OC device temperature of the OC device; 
 a control logic for determining if the OC device is operating at the specified temperature range; and 
 a control logic for adjusting at least one operating parameter of the internal combustion engine for controlling the exhaust gas temperature such that the OC device is below the specified temperature range, wherein the at least one parameter of the internal combustion engine is adjusted if the SCR device is above the light-off temperature and if the OC device is operating at the specified temperature range. 
 
 
     
     
       17. The exhaust gas treatment system as recited in  claim 16 , further comprising an electrically heated catalyst (“EHC”) device in fluid communication with the exhaust gas conduit and configured to receive the exhaust gas, wherein the EHC device is located within the OC device and is selectively activated to produce heat and induce further oxidation of the exhaust gas. 
     
     
       18. The exhaust gas treatment system as recited in  claim 17 , wherein the control module is in communication with the EHC device, and wherein the control module includes control logic for deactivating the EHC device if the SCR device is above the light-off temperature. 
     
     
       19. The exhaust gas treatment system as recited in  claim 16 , comprising a hydrocarbon injector connected to and in fluid communication with the exhaust gas conduit, wherein the hydrocarbon injector is selectively activated for delivery of a hydrocarbon and formation of an exhaust gas and hydrocarbon mixture therein, and wherein the control module is in communication with the hydrocarbon injector, and the control module includes control logic for deactivating the hydrocarbon injector if the SCR device is above the light-off temperature and if the OC device is operating at the specified temperature range.